Was in this same situation about 7 years ago, with sub zero temps.
No ice or snow on Rig but slides were frozen shut.
I have same problem as Jim this year, and will not even attempt to open slides for fear of damaging something or not getting the slides back in.
The weather here has been brutal, it hasn't even gotten above 12 degrees here for a high in a week, nights are below zero.
Thursday and Friday this week the highs will be 6 both days, and way below zero for lows.
7 years ago, we loaded fridge the morning we left, and went from Port Huron, Michigan to Racoon Valley, TN for first nights stop and everything in the fridge was frozen.
It didn't get above 10 until we were in Southern Kentucky.
We can get into our bedroom through the bathroom, so we will put some things on the bed, the rest on floor by the door.
We will buy anything that might freeze when we get to our destination.
We were watching the 10 day extended forecast for weeks and when the sub zero popped up on the weather we loaded all our clothes and non freeze able things into trailer before it got real cold.
I also loaded the box of my truck with the things I was taking South.
I have about 20 cities programmed into my weather app, so I monitor my entire route South for weather.
We only have minimal things to put in when we leave.
This will be our first year of ever staying in a motel when we have the trailer on.
We are stopping in Bowling Green, Kentucky the first night.
We usually stay in Cave Country RV Park, but this year only going to be 7 degrees that night, and figured the furnace will run constantly, so we decided to travel about 35 miles farther and stay in Bowling Green.
My suggestion is, if you don't need to open your slides don't, or run your furnace as Gaffer said, but remember, it may run constantly and suck up all your Propane.
We are experiencing some very brutal weather.
Hope this may have helped you some, or have given you some ideas.
One more thought, check your tires, because of the extreme cold, your pressure will be low.
Good luck my friend, safe travels, stay warm, & hope to see you in Ludington.
Hockster